Modern advances in digital information and data processing technology have made it scientifically and economically feasible to extend digital imaging techniques into a broader range of radiographic applications. In particular, digital radiographic imaging has developed into an accepted modality for many X-ray applications, such as angiography.
It is known, for example, to couple Vidicon or Isocon cameras to a fluorescent X-ray screen and digitize the analog output of the camera. Among other advantages over conventional intensifying screen and film methods, digital processing techniques have helped reduce patient risk by reducing patient dosage due to greater detection efficiency of the X-ray receptors, by using the greater dynamic range of image intensifier camera units to reduce the amounts of contrast material, and by allowing image post-processing to remove overlying structures or distracting background (viz., subtraction techniques). However, these systems, because of their inherent slow reaction time have problems such as image misrepresentation due to patient motion between frames.
Digital linear slit scanning units for chest radiographic applications are known in the art. These units are generally dedicated devices consisting of an X-ray tube, a slit aperture, and photodiode detector elements. Low dose, single beam, spot scanning systems are also known and available on a commercial basis.
Also known in the prior art are multiple slit rotating disk systems for scatter reduction in film-based radiography. More recently, a scanning system has been described which would consist of a rotating, multiple-slit, cone-shaped X-ray aperture mechanism co-ordinated with a rotating cone having linear photodiode arrays mounted thereon as detectors. Such a system may provide greater scan uniformity and higher scan rates than the linear scan units.
All of the known systems described above offer the advantages of a wider dynamic range than is available with film-based radiography and a reduction in the level of scattered radiation detected after passing through the target. Linear scanning units, however, have limited spatial resolution and relatively slow scan times (on the order of 4 seconds). Image quality can be severely affected by patient motion during the relatively long scanning times required. For many radiographic applications, e.g., chest scans, scoleosis, or fractures, high resolution is not necessary. In addition, in such units scan uniformity problems may exist since the X-ray scanning slits and detectors are "stepped" past the patient (rather than moved continuously). Similar restrictions apply to the imaging capabilities of a spot scanning system. Although the rotating multi-slit concentric cone concept should not encounter scan motion uniformity problems and technically should be capable of multiple frame per second scan rates, such a system will require a permanent installation and have high construction costs for the rotating cones and the fiberoptic minifiber detector arrays proposed. The physical size and expense of such a device makes wide-spread acceptance in a general clinical setting prohibitive.
In passing, reference is made to U.S. Pat. Nos. 2,730,566, 4,315,146 and 4,398,302, which illustrate the prior art arrangements as mentioned hereinabove and which are subject to significant drawbacks.
Accordingly, the principal object of the present invention is to improve subject contrast in X-ray imaging due to scatter effect removal using slit scanning and detecting techniques.
Another object of the present invention is to provide the advantage of the wide dynamic range available from photodiode arrays, along with adequate spatial resolution.
A further object is to provide a system with variable scan times appropriate for many radiographic applications.
Yet another object of the present invention to provide a system adaptable to use in a general clinical setting.